GB2309653A - Manufacture of bituminous materials by drying, screening and mixing - Google Patents

Abstract

Desired quantities of selected aggregate materials and sand are delivered from storage bins (12, Fig 1) to a dryer 17 by means of a conveyor (15, Fig 1) on which sand forms the first layer and aggregate as superposed layers. Within the dryer, a contraflow of heated air dries the materials which are then delivered to a screen stack 32 which separates the material into a number of hoppers 35 each containing material of different size. Selected materials are discharged into a weigher 35 which weighs a batch of materials for delivery to a mixer 38. Liquid bitumen is injected into the mixer from a spray bars 43 or 95 and mixed with the materials to form a bituminous composition. The mixer discharges the bituminous composition into a collection truck 50 which runs along an inclined track 52 to deliver the composition to storage silos.

Description

eManufacture of bituminous materials This invention relates to a process and apparatus for the manufacture of bituminous materials.

The invention is particularly concerned with the manufacture of bituminous materials in an efficient and trouble-free manner.

According to the invention there is provided a process for manufacturing bituminous materials, comprising the steps: discharging in a controlled manner desired quantities of sand and a number of selected aggregate materials of different size from associated storage bins onto a feed conveyor for delivery to a dryer, discharging a layer of sand first onto the feed conveyor and then discharging the selected aggregate materials onto the sand on the feed conveyor forming a number of superimposed layers of sand and aggregate materials on the feed conveyor, passing the sand and aggregate materials through the dryer for drying the sand and aggregate materials by passing heated air through the dryer in contra-flow to the sand and aggregate materials, extracting the heated air from an inlet of the dryer, filtering the heated air and collecting dust filtered from the heated air, delivering the sand and aggregate materials from the dryer to a screen stack, screening the sand and aggregate materials for separating the sand and aggregate materials into a number of hoppers each containing material of different pre-desired size, delivering preset amounts of selected materials from the hoppers to a weigher, discharging material from the weigher into a mixer, spraying a measured amount of liquid bitumen into the mixer, mixing the liquid bitumen with the materials in the mixer to form a bituminous composition, and discharging the bituminous composition into a collection truck beneath the mixer.

In one embodiment of the invention the liquid bitumen comprises a mixture of bitumen and Trinidad Lake asphalt and includes the steps: delivering pre-selected quantities of bitumen and Trinidad Lake asphalt into a blender, blending the bitumen and the Trinidad Lake asphalt at a pre-set temperature to form an homogenous bitumen puree, delivering the bitumen puree into a weighing cup suspended on load cells for collecting a desired weight of bitumen puree at a pre-set temperature in the weighing cup, opening an outlet of the weighing cup and discharging the bitumen puree into a collecting pan within which the weighing cup is mounted, feeding the bitumen puree from the collecting pan to a spray bar mounted within the mixer for spraying the bitumen puree onto the materials in the mixer.

In another embodiment the process includes breaking up used asphalt material in a crusher for reducing the used asphalt material to pieces of less than 20mm size, and feeding a measured quantity of used asphalt pieces into the mixer with the materials from the hoppers.

In a preferred embodiment up to 5% by weight of used asphalt material is delivered to the mixer with each batch of material.

In a particularly preferred embodiment the process includes driving the collection truck along an upwardly inclined track extending over a number of insulated storage silos mounted beneath the track, positioning the truck above an inlet of a selected storage silo and discharging the bituminous composition from the truck into the storage silo.

In another embodiment, the process includes the step of adding a preselected amount of the filtered dust to the materials in the weigher.

In a further embodiment, the process includes filtering the heated air extracted from the dryer by delivering the heated air through a coarse filter and then through a fine filter downstream of the coarse filter.

In a particularly preferred embodiment, the dryer comprises a rotating cylindrical drum supported on two pairs of rotating rollers which engage complementary circumferential drive rings on the drum, drive being transmitted from at least one drive motor through at least one roller to a drive ring for rotating the drum.

The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of apparatus used in a process according to the invention for the manufacture of bituminous materials; Fig. 2 is a perspective view of a dryer used in the process; Fig. 3 is a schematic elevational view of portion of the apparatus; Fig. 4 is a diagrammatic side elevational view of portion of the apparatus; and Fig. 5 is a detail perspective view of a weighing kettle forming portion of the apparatus.

Referring to the drawings a process and apparatus for the manufacture of bituminous materials according to the invention will be described.

Aggregate materials are received at an intake hopper 10 and delivered by a conveyer 11 to one of a number of aggregate storage bins 12.

An outlet 14 from each storage bin 12 is operable to deliver aggregate material onto a feed conveyor 15 for delivery of aggregate material onto a transfer conveyer 16 communicating with an inlet of a dryer 17. It will be noted that larger aggregates are stored in bins 12 adjacent the transfer conveyer 16, aggregate size getting progressively smaller in the bins as one moves away from the transfer conveyer 16, with sand being stored in the outermost bin 12. In this way when aggregate materials for a mix are selected sand is first deposited on the belt of the feed conveyer 15 to form a protective cover and as the conveyer 15 moves towards the transfer conveyer 16 progressively larger aggregate material is built up in a number of superimposed layers on the belt of the feed conveyer 15.

The dryer 17 comprises a cylindrical drum 20 rotatably mounted on a support frame 21 by means of pairs of rollers 22 which engage circumferential drive rings 23 adjacent opposite ends of the drum 20. Rollers 22 at opposite ends of the drum 20 are driven by motors 24, friction drive being transmitted through the rollers 22 to the rings 23 to rotate the drum 20. It will be appreciated that, advantageously this is a relatively quiet drive mechanism for the drum.

Heated air is delivered in contra-flow to the aggregate materials through the drum 20. The heated air is extracted from the dryer inlet and delivered through a cyclone type coarse filter 25 in which larger dust particles are removed from the air. Air discharged from the coarse filter 25 is passed through fine filters 26 containing filter bags through which the air is delivered, fine dust dropping to the bottom of the fine filters 26 from which it is discharged and collected in a filler tank 27. Desired quantities of the filler material can be added to the weigher with the aggregate materials subsequently in the process as is described later. An additional filler tank 28 is also provided to make up any required amounts of filler in selected mixes.

Dried aggregate material discharged from an outlet 29 of the dryer 17 is carried away by an elevator 30 and discharged onto a screen stack 32 for separating the dried aggregate material into aggregate holding bins 33 each containing aggregate material of different size. It will be noted that the screen stack and the holding bins 33 are insulated for retention of heat imparted to the aggregate material in the dryer 17. The insulation also advantageously suppresses noise.

Mounted directly below the holding bins 33 is a weigher 35. Desired quantities of selected sand and aggregate materials are delivered in turn from a number of the holding bins 33 into the weigher 35 for cumulatively weighing a batch of aggregate material for an asphalt mix.

The collected material is then discharged from the weigher 35 into a mixer 38 mounted directly below the weigher 35.

Liquid bitumen is heated to a desired temperature and pumped from a storage tank 40 through a flow meter 42 to a spray bar 43 located within the mixer 38. The spray bar 43 has a number of spaced-apart nozzles for spraying the liquid bitumen onto the aggregate within the mixer 38. A pair of juxtaposed mixing paddles 45 mounted at a lower end of the mixer 38 and driven by an external motor 46 are operable to mix the liquid bitumen with the aggregate materials to form the desired asphalt composition.

When thoroughly mixed doors at a bottom 48 of the mixer 38 open for discharge of the asphalt composition into a truck 50 positioned directly beneath the doors. It will be noted that the controls for the doors are connected to the controls for the truck 50 such that the doors cannot open unless the truck 50 is located directly beneath the doors.

The truck 50 is mounted on inclined tracks 52. A cable 53 attached to the truck 50 passes over a pulley 54 at an upper end of the track 52 and down to a winch 55 operable for reeling the cable 53 to move the truck 50 up and down the track 52 for positioning the truck 50 over one of a number of insulated asphalt storage silos 58 arranged in a row beneath the track 52. When the truck 50 is positioned over a selected silo 58 an outlet door in a base of the truck 50 opens for discharge of asphalt into the silo 58, as shown in broken outline in Fig. 4.

Referring to Fig. 4 a lower portion 60 of the track 52 is hinged at 61. If desired the truck 50 can be positioned above the hinge 61 and the lower portion 60 raised, as shown in broken outline, to a horizontal position for discharging the asphalt directly into a vehicle manoeuvred beneath the mixer 38.

An outlet 64 at a lower end of each silo 58 is positioned above a truck loading bay 65 beneath each silo 58.

In some cases the liquid bitumen comprises a mixture of bitumen and Trinidad Lake asphalt. This mixture is highly corrosive and cannot be handled by the flow meter due to the abrasive filler content of Trinidad Lake asphalt. In this instance the desired quantity of the bitumen mixture is measured in a weigh kettle 70 shown in Fig. 5. The weigh kettle 70 has a weighing cup 71 which is suspended on load cells. An outlet 72 at a bottom of the cup 71 is closable be means of a plug 73. The plug 73 has an upstanding spindle 74 which connects via a pivot linkage 75 with a ram 76 for raising and lowering the plug 73 to open and close the outlet 72. The pivot linkage 75 comprises a lever 78 pivotably mounted intermediate its ends by a pivot pin 79 mounted on a support bracket 80.

An outer end of the lever 78 is connected to the ram 76.

An inner end 82 of the lever 78 connects through a slotted link 83 with an upper end 84 of the spindle 74. The slotted link 83 ensures only the weight of the plug 73 and spindle 74 is measured when weighing the cup 71. A supply pipe 85 delivers a heated puree of the bitumen and Trinidad Lake asphalt through a supply valve 86 into the cup 71. The supply valve 86 is operable to deposit a major portion of the puree into the cup 71 and then trickles the remainder up to a desired weight as measured by the load cells. Mounted around the cup 71 is a collecting pan 90 having an oil heated jacket with associated heating tape 92. A measured batch of puree discharged from the cup 71 collects in the pan 90 and is gravity fed through a discharge pipe 94 into a spray bar 95 located within the mixer 38.The spray bar 95 has a number of elongate slots for discharge of the bitumen puree into the mixer 38 for mixture with the aggregates.

It will be appreciated that the invention provides a process and apparatus for the preparation of bituminous materials in an efficient and trouble-free manner. The manner of feeding materials to the dryer minimises wear on the conveyor and reduces the risk of breakdown. The construction of the dryer advantageously allows the dryer to be operated in a relatively quiet fashion. Filtering dust from the dryer and recycling the dust in the process both improves efficiency of the process and eliminates the problem of pollution if the dust were to be discharged into the atmosphere. Further, the insulation of the screen stack and holding bins advantageously both retains heat in the aggregate materials and also dampens the noise of the materials as the materials are delivered through the apparatus. Corrosive asphalt materials are also handled and accurately metered by means of the weight kettle, promoting trouble-free operation of the process.

Also, the arrangement of the collection truck on the inclined rails allows for rapid throughput of batches of bituminous material in the mixer by quick and efficient emptying of mixed material from the mixer.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims (10)

1. A process for manufacturing bituminous materials, comprising the steps: discharging in a controlled manner desired quantities of sand and a number of selected aggregate materials of different size from associated storage bins onto a feed conveyor for delivery to a dryer, discharging a layer of sand first onto the feed conveyor and then discharging the selected aggregate materials onto the sand on the feed conveyor forming a number of superimposed layers of sand and aggregate materials on the feed conveyor, passing the sand and aggregate materials through the dryer for drying the sand and aggregate materials by passing heated air through the dryer in contra-flow to the sand and aggregate materials, extracting the heated air from an inlet of the dryer, filtering the heated air and collecting dust filtered from the heated air, delivering the sand and aggregate materials from the dryer to a screen stack, screening the sand and aggregate materials for separating the sand and aggregate materials into a number of hoppers each containing material of different pre-desired size, delivering preset amounts of selected materials from the hoppers to a weigher, discharging material from the weigher into a mixer, spraying a measured amount of liquid bitumen into the mixer, mixing the liquid bitumen with the materials in the mixer to form a bituminous composition, and discharging the bituminous composition into a collection truck beneath the mixer.

2. A process as claimed in claim 1, wherein the liquid bitumen comprises a mixture of bitumen and Trinidad Lake asphalt and includes the steps: delivering pre-selected quantities of bitumen and Trinidad Lake asphalt into a blender, blending the bitumen and the Trinidad Lake asphalt at a pre-set temperature to form an homogenous bitumen puree, delivering the bitumen puree into a weighing cup suspended on load cells for collecting a desired weight of bitumen puree at a pre-set temperature in the weighing cup, opening an outlet of the weighing cup and discharging the bitumen puree into a collecting pan within which the weighing cup is mounted, feeding the bitumen puree from the collecting pan to a spray bar mounted within the mixer for spraying the bitumen puree onto the materials in the mixer.

3. A process as claimed in claim 1 or 2, wherein the process includes breaking up used asphalt material in a crusher for reducing the used asphalt material to pieces of less than 20mm size, and feeding a measured quantity of used asphalt pieces into the mixer with the materials from the hoppers.

4. A process as claimed in claim 3, wherein up to 5% by weight of used asphalt material is delivered to the mixer with each batch of material.

5. A process as claimed in any preceding claim wherein the process includes driving the collection truck along an upwardly inclined track extending over a number of insulated storage silos mounted beneath the track, positioning the truck above an inlet of a selected storage silo and discharging the bituminous composition from the truck into the storage silo.

6. A process as claimed in any preceding claim including the step of adding a preselected amount of the filtered dust to the materials in the weigher.

7. A process as claimed in any preceding claim which includes filtering the heated air extracted from the dryer by delivering the heated air through a coarse filter and then through a fine filter downstream of the coarse filter.

8. A process as claimed in any preceding claim wherein the dryer comprises a rotating cylindrical drum supported on two pairs of rotating rollers which engage complementary circumferential drive rings on the drum, drive being transmitted from at least one drive motor through at least one roller to a drive ring for rotating the drum.

9. A process for the manufacture of bituminous material substantially as hereinbefore described with reference to the accompanying drawings.

10. Bituminous materials whenever produced according to the process as claimed in any preceding claim.